Dust proof switch mechanism



Dec. 10, 1957 E. STAAK ETAL 2,816,199

DUST PROOF SWITCH MECHANDISM Filed Dec. 27, 1955 J/n l erz tor-s:

A 041119 E .Staa/z:

6/49/21? 0. VV/W/ZS by United States Patent DUST PROOF swrrcn MECHANISM Louis E. Staalr, Fort Wayne, and Glenn D. Willits, Leo,

Ind., assignors to General Electric Company, a corporation of New York i Application December 27, E55, Serial No. 555,398

2 Claims. (Cl. 200-168) This invention relates to electric switch mechanisms, and more particularly to a dust-proof switch especially suited for use in dynamoelectric machines to be operated in atmospheres having a considerable amount of dust therein.

Electrical switch mechanisms are dependent for their continued proper operation upon positive electrical engagement of the switch contacts when they are brought together. When such contacts are operated in atmospheres containing a considerable amount o'f dust, the effective life of the switch mechanism is greatly shortened unless the contacts are frequently cleaned to remove the dust. Where the dust is of a generally insulating nature, it will cause the contacts to fail to complete an electrical circuit when they are brought together. An equally undesirable result is obtained where the dust is of a conductive nature, since the contacts generally are separated onlya small amount and conductive dust may cause short circuiting between the contacts even when. they are in open position. Failure of the switch to operate properly becomes particularly objectionable in the case of dynamoelectric machines such as electric motors where, for instance, the operation of the switch controls the energization of a motor winding. In such a case, and more particularly in the case of single phase self-starting alternating current induction motors where the closing of the switch effects energization of a winding to start a motor and it is subsequently intended that the switch be opened when the motor has come up to speed, the results of faulty operation of the switch can be disastrous. If the contacts fail to complete the circuit in their closed position, no circuit will be completed to the winding. However, in such cases, there is generally a circuit completed to another winding independently of the switch, and in such an event, where the switch fails to energize the second winding, the motor will not start and the other winding may burn out. On the other hand, if the switch fails to open once it has closed, due to the short circuiting effect of dust, the second winding which normally is built for intermittent energization only will be energized continuously and will then burn out.

For these reasons, it is most desirable to prevent the access of dust to the contacts of a switch, particularly where used in such a motor. However, the contacts are usually operated by means responsive to the speed of the motor so as to disconnect the second winding at a predetermined speed. The usual mechanisms provided to effect this action are generally exceedingly sensitive, and any appreciable force opposing or' aiding their action will cause operation of the switch at a speed far removed from that desired. Therefore, it is most desirable that the insulation of the contacts from a dust filled atmosphere be effected without any substantial force being applied in any manner so as to modify the action of the switch.

It is, therefore, an object of this invention to provide "ice an improved switch mechanism which will incorporate the desirable features set forth above.

Further objects and advantages of this invention will become apparent and the invention will be better understood by reference to the following description and the accompanying drawing, and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In its broader aspects, the invention provides a switch mechanism which includes a pair of relatively movable contacts arms, with a pair of contacts respectively mechanically and electrically secured to the arms and positioned to be in engagement at a predetermined relationship of the arms. A tubular member formed from a thin sheet of highly flexible insulating material is secured to at least one of the arms and extends between the arms into contact therewith so as to enclose the contacts. The engagement of the tubular member with the contact arm precludes the access of the dust filled atmosphere to the contacts. The provision of a highly-flexible insulating material in the form of a thin sheet eliminates to a considerable extent any resilient qualities the material may have, and permits the arms to be moved relative to each other with the application of only a minute force from the insulating material so as to effect no substantial modification of the action of the switch in response to the speed responsive device.

In the drawing, Figure 1 is a fragmentary side view, partly in cross section, of the improved switch device of this invention in closed position in use in a dynamoelectric machine;

Figure 2 is a view similar to Figure l, with the switch mechanism in its open position; and v Figure 3 is an exploded view in perspective of the improved switch mechanism.

Referring now to the figures of the drawing, there is shown the rotor 1 of an electric motor of the induction type formed, as is customary, of a stacked plurality 2 of thin laminations of magnetic material with an end ring 3 at each end to interconnect the conductors (not shown) which extend through the stack 2 of laminations. Rigidly secured to the rotor 1 is a shaft 4, and a member 5 having a cushioning pad 6 attached thereto is secured about the shaft. A pair of weight members 7 are respectively mounted on flange portions 8 formed at opposite ends of member 5. Each weight member 7 has a pair of arms 9 (only one is shown); springs 10 are secured between the opposing arms 9 of the members 7 respectively so as to tend to pull them together and maintain the weight members 7 in the position shown in Figure 1. An extension 11 on each weight member is pivotably mounted in an opening 12 provided in a sleeve member 13 which is slidably mounted on shaft 4. In the position of Figure l, extensions 11 force the sleeve member into abutment with a resilient portion 14 of a contact arm 15. When rotor 1 and shaft 4 reach a predetermined speed of rotation, weight members 7 will move outwardly to the position shown in Figure 2. In this position, extensions 11 will have pivoted within opening 12 of sleeve member 13 and will have pulled the sleeve member to the right along the shaft out of engagement with portion 14 of contact arm 15. The func tioning of the centrifugal mechanism set forth above is more fully described in Patent 2,149,108, issued to Alfred P. Welch on February 28, 1939 and assigned to the assignee of the present application. It will be understood that the rotor structure and the centrifugal device have been set forth in some detail for illustrative purposes, and that the structure described does not form a part of the present invention.

Contact arm 15 is secured to a terminal board 16 I 3 and may be arranged in electrical engagement with a member 17, as shown. A contact 18 is secured to contact arm 15 and is arranged to engage a contact 19 secured to a contact arm 20 which is fastened to the terminal board 16 at 21 by conductive means 22 so that an appropriate electrical conductor (not shown) may be secured thereto. Contact arm 15 has openings 23 formed therein on opposite side of contact 18. A tubular member 24 formed from a thin sheet of highly flexible insulating material (such as, for instance, silicone rubber) has a pair of lugs 25 formed to extend from end 26 thereof. The lugs are forced through the openings 23 respectively so as to secure the tubular member 24-with its end 26 against the surface 2'7 of contact arm 15. Tubular member 24 is closed at its other end 28 and is provided with a slot 29 which is formed slightly smaller than contact arm 20 and contact 19 so that the contact 19 may be forced through the slot 29 and the edges of the slot will then be in tight dust-proof contact with the contact arm 20. When the contact arms 15 and 20 and the tubular member 24 are assembled in this manner, as best seen in Figures 1 and 2, the two contacts are entirely enclosed because of the tubular member extending between the contact arms on which the contacts are mounted.

The thinness of the sheet of flexible material provides tubular member 24 with a considerable degree of flexibility without any substantial corresponding resilience. This is a most desirable feature since otherwise there would be a positive force effecting a modification of the speed at which the centrifugal mechanism would operate. In addition, the configuration of the member 24 and its association with the contact arms provide a dustfree enclosure for the contacts.

While this invention has been explained by describing a particular embodiment thereof, it will be apparent that improvements and modifications may be made without 4 departing from the scope of the invention as set forth in the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A switch mechanism comprising a pair of relatively movable contact arms, a pair of contacts respectively mechanically and electrically secured to said arms and positioned to be in engagement at a predetermined relationship of said arms, and a tubular member formed from a thin sheet of highly flexible insulating material having an open end and a closed end, said open end being arranged over one of said contacts against the arm secured thereto, said tubular member having a slot formed therein in spaced relation to said open end, the other of said arms extending through said slot in tight relation therewith with that one of said contacts secured thereto within said tubular member whereby both said contacts are enclosed. 2. A switch mechanism comprising a pair of relatively movable contact arms, a pair of contacts respectively mechanically and electrically secured to said arms and positioned to be in engagement at a predetermined relationship of said arms, and a tubular member formed from a thin sheet of highly flexible insulating material having an open end and a closed end, said open end being arranged over one of said contacts against the arm secured thereto, said tubular member having a slot formed therein intermediate said ends, the other of said arms extending through said slot in tight relation therewith with that one of said contacts secured thereto within said tubular member whereby both said contacts are enclosed.

References Cited in the file of this patent UNITED STATES PATENTS 

